1. Field of the Invention
The present invention relates to fuel injectors for internal combustion engines, and particularly to improvements in accumulator-type fuel injectors, including both unintensified and intensified accumulator injectors, which produce improved fuel economy, noise reduction, and reduction of undesirable exhaust emissions, including smoke, oxides of nitrogen, and hydrocarbons.
2. Description of the Prior Art
Accumulator-type fuel injectors have been known in the art for many years, but never have achieved widespread use. It is believed this is because they have heretofore not solved problems present in conventional injectors, and have even introduced additional problems which have been inherent in prior art forms of accumulator injectors.
One serious problem with both conventional fuel injectors and prior art accumulator-type fuel injectors has been premixed burning of the fuel. Typically, about 25-50 percent of the total quantity of fuel injected will be atomized and mixed with air prior to the start of combustion. The sudden combustion of this premixed fuel causes a rapid rate of heat release at the beginning of ignition, with a resulting excessively high noise level, and undesirable exhaust emissions including smoke, oxides of nitrogen, and hydrocarbon emissions. One answer to this problem is to provide a two-stage injection, with a small pilot charge of fuel first injected and ignited, and then the main charge of fuel injected and immediately ignited by the already ignited pilot charge. A system of this type is taught in Loyd U.S. Pat. No. 4,414,940. Although the Loyd system does solve the problem, it requires two separate injectors, one for the pilot charge and another for the main charge, making the system undesirably complicated and expensive.
Another problem with both conventional fuel injectors and prior art accumulator-type fuel injectors is that they produce a fixed spray pattern regardless of engine power demands, and this necessarily compromises engine efficiency at some power settings. For optimum overall engine efficiency, it would be desirable to tailor the spray configuration variably according to the power demands of the engine by having a relatively wide, flat conical spray configuration at relatively low fuel delivery, such as during engine idle, and to have the cone of the spray narrow progressively as the power setting is progressively increased.
The injector needle closure event has been characteristically unsatisfactory in prior art accumulator-type injectors. Typically, atomization of the fuel has been poor as the needle approaches the seat. Rapid needle closure is required to keep atomization good during the closing event, but the required high speed needle movement has caused needle bounce off of the seat, resulting in secondary and sometimes tertiary injection events, with essentially unatomized fuel dribble being the further result. Both poor atomization and fuel dribble associated with needle closing results in undesirable smoke and high hydrocarbon levels in the exhaust. Prior art accumulator needles have been characteristically long and massive, and if closed at high speed, considerable elastic compressional energy builds up along their lengths upon striking the valve seat, and when this energy is released it causes the needle to bounce off the seat. Examples of accumulator injector needles which are thus undesirably long and massive are found in Falberg U.S. Pat. No. 2,985,378, Berchtold U.S. Pat. No. 4,566,416, Loyd U.S. Pat. No. 4,414,940, Beck et al, U.S. Pat. No. 4,628,881, Vincent et al. U.S. Pat. No. 4,080,942, and in a 1957 publication by Hooker in the Volume 65, 1957 issue of "SAE Transactions," illustrated at page 317. The typical accumulator injector needle mass is on the order of about six grams or more, and with this much mass the energy of momentum of a fast-closing needle is generally too much to avoid needle bounce.
Such prior art long needles in accumulator-type injectors also resulted in an undesirably large needle column length for compression when the injector was charged prior to injection, which tended to prevent close control of the injection characteristics.
While a short, very lightweight needle is desirable to minimize needle bounce, needle closure damping associated with such short, lightweight needle is also desirable to positively preclude needle bounce in a high speed needle closing event. Applicants are not aware of such closure damping having been addressed in the prior art. It is believed that this is because the prior art has not sought to cure the problem of poor atomization proximate needle closure by means of a high speed needle closing event.
In order to maintain good atomization right up to needle closure, it is also necessary to have a high closing accumulator pressure, and this in turn requires high peak pressure and high average pressure in the accumulator cavity to get the required injection quantity at high power settings. A relatively small accumulator cavity is required for high accumulator pressures. Conventional accumulator injector practice has been to have the accumulator cavity coaxially disposed around the needle, with the needle closure spring disposed within the accumulator cavity. In general, this results in accumulator cavities which are too large for a high pressure accumulator, particularly with the very high pressure in an intensified-type accumulator injector such as that disclosed in the aforesaid Beck et al. U.S. Pat. No. 4,628,881. With the spring located in the accumulator cavity, the only way to reduce the volume of the cavity would be to reduce the size of the spring, and this is just the opposite off what is required for high speed needle closure, namely, a large, strong closure spring. This conventional arrangement with the needle spring concentrically located within the accumulator cavity is seen in Falberg U.S. Pat. No. 2,985,378, Berchtold U.S. Pat. No. 4,566,416, Loyd U.S. Pat. No. 4,414,940, Beck et al. U.S. Pat. No. 4,628,881, and the aforesaid Hooker publication. Vincent et al. U.S. Pat. No. 4,080,942 has the needle spring located in a control chamber which receives pressurized fluid for holding the needle down, but this has resulted in the main accumulator chamber being spaced coaxially above the control chamber, a cumbersome arrangement which could not possible be used in an intensified form of accumulator injector such as that disclosed in the Beck et al. U.S. Pat. No. 4,628,881. For a practical and compact accumulator fuel injector, the accumulator cavity should be arranged closely proximate the spring cavity within a lower portion of the injector, and generally concentrically and thereby compactly oriented about the spring cavity. This is the only feasible location for the accumulator cavity in an intensified form of accumulator injector.
Pintle spray nozzles have frusto-conical deflecting surfaces are known in the fuel injector art, and are common in garden hose nozzles. In hose nozzles, the angle of the spray is manually adjustable by axial movement of the pintle head relative to the orifice. However, no such adjustability has heretofore been known in the fuel injector art, even though automatic adjustment of the spray cone angle to tailor the spray to engine power demands could produce substantial increases in efficiency over the engine power spectrum.
Two-stage injection processes are better suited for the reduction of undesired premixed burning when the injection of the initial or pilot charge is throttled to produce a highly atomized and dispersed pre-injection spray for ignition and the main charge is injected in the form of a penetrating jet spray. The atomized initial charge is produced by forcing the fuel under high pressure through a small area immediately upstream of the injection holes so as to produce highly turbulent flow through the holes, thus resulting in the desired atomization. This effect, however, cannot be achieved substantially using conventional sac or pintle nozzles.
Another problem associated with conventional two-stage fuel injection systems is that such systems typically cannot be converted into single-stage systems, i.e., systems lacking a pilot or initial injection stage, without completely redesigning the system. This of course limits the versatility of the typical two-stage injection system.